Beamforming is performed in wireless communication systems to facilitate the enhancement of communications exchanged between communicating entities, and the rejection of signals that interfere with the communications.
Determining the DOA of beams received from the communicating entities is fundamental to correctly orienting a boresight of the beams and, using an appropriate beam width, power, and other settings, and maximizing the performance of one communication link while minimizing interference to other links.
An example of a conventional wireless communication system that determines the DOA is U.S. Pat. No. 6,650,910 entitled “Methods and Apparatus in Antenna Diversity Systems for Estimation of Direction of Arrival”, which issued to Mazur et al., (hereinafter referred to as “Mazur”), on Nov. 18, 2003. The system disclosed by Mazur is capable of deducing the DOA in one plane of incidence. However, Mazur's system is capable of determining only the direction of the beam within a two-dimensional plane at a right angle to the antenna array.
An adaptive antenna generates a set of antenna beams such that each beam covers a narrow predefined area and the beams together cover a wide predefined area omni-directionally or within a sector. A signal sent from a transmitter is received by each of the antenna beams, and each signal is processed to calculate the angular information. The angular information is inherent in the phase difference between different versions of the signal. A DOA estimation of the direction to the signal source is made on the basis of the demodulated versions of the received signal.
Conventional wireless communication systems estimate DOA in the context of azimuth only, such as with Butler matrix implementations as disclosed by Mazur. The prior art does not take into account beamforming differing in three-dimensional space. There is no resolution in the elevation domain in conventional wireless communication systems. The beam must therefore be of such a width in elevation that it adequately intersects with the target's antenna pattern.
FIG. 1 illustrates the disadvantages of restricting the formation of beams, formed by a transmitter 100, to two dimensions 105 and 110, (i.e., one plane), in a conventional wireless communication system including the transmitter 100 and a receiver 120 having an antenna 215. Any given plane is defined by two dimensions. For example, a general volume of space is defined by coordinates x, y, and z. A plane may be defined by selecting any two of the coordinates, say x and y. This plane contains all of the possible values of z. The prior art can operate in a plane using any of two of these dimensional pairs, or a plane skewed from the three orthogonal directions. However, there will always be a plane remaining with indeterminate values, which may or may not be parallel to a fixed orientation. Alternatively, the coordinate system could be rotated to make a plane parallel in two of the directions.
When beam adjustments are made to the beams 105 and 110 shown in the azimuth view of FIG. 1, there is no elevation adjustment of the boresight, as demonstrated by the beams 105 and 110 shown as having the same orientation in the elevation view of FIG. 1. Thus, the beam width is wider in the elevation dimension, with a corresponding need for a higher gain factor. This results in an excessive usage of power by the transmitter 100, and more interference to devices not involved in the link.
Assuming that the transmitter 100 and the receiver 120 are transceivers which communicate via a wireless link, when the direction of beam transmission between the transceiver 100 and the transceiver 120 are reversed, (i.e., transceiver 100 is receiving and transceiver 120 is transmitting), beams similar to those shown in FIG. 1 are formed by the transceiver 100 for the reception of signals without allowing for elevation adjustment of the boresight. However, this may cause an excessive number of signals that are not associated with the link to be received.